Hard X-ray Diagnostics of Solar Eruptions H. Hudson SSL, UC Berkeley and U. Of Glasgow

Background information Meter-wave radio phenomena require (types I-V etc.) require non-thermal electrons. These also emit X-ray bremsstrahlung, but not very efficiently (~10 -5 ). With the X-rays, we can study energetics more directly. Limb occultation, plus imagers on Yohkoh and RHESSI have greatly expanded our knowledge. See Krucker et al., A&A Rev 16, 155 (2008) for full details.

History I March 30, 1969 occultation event (OSO-5; Frost & Dennis 1971) Two occultation events observed by OSO-7 (Hudson 1978; Hudson et al. 1982) Direct imaging: Hinotori May 13, 1981 Stereoscopic observations: Kane, 1983 CME significance: Kiplinger 1995 Moving coronal source: Hudson et al RHESSI: Krucker et al., A&A Rev 16, 155 (2008) for full details of many events

Limb occultation McKenzie, 1975 SOL

History II Frost & Dennis 1971 Palmer & Smerd 1972 Kawabata et al Hudson et al Hudson et al Kane 1983

Coronal Hard X-ray Sources SOL : Yohkoh/SXT observation, keV, occultation height ~88 Mm. For this event one could infer that the non-thermal pressure dominated the core plasma pressure (Hudson et al. 2001). SOL : RHESSI observation, keV, occultation height ~100 Mm (Krucker et al. 2007). This event was also see on-disk from a Mars perspective. SOL : RHESSI observation, keV, height ~40 Mm (Krucker et al. 2008). With RHESSI imaging one does not absolutely need the accident of occultation since we can just use projection to get a crude altitude. These high photon energies are remarkable and imply a highly non-thermal plasma inclusion in the corona.

RHESSI Occultation Event Observations of SOL reported by Krucker et al. (2010). Thin-target bremsstrahlung observations require rapid heating: dT/dt = 4.5 n 9 -1 keV s -1. For the observed limit on ambient density, this source requires dT/dt ~ 5 MK/s. This is faster than the Coulomb (e,p) relaxation can permit, and so there is no core thermal distribution for electrons in this plasma.

Particles and Energetics Electron acceleration to >10 keV (to ~100 kT) dominates the impulsive- phase energy release (Kane & Donnelly, 1971; Brown, 1971; Hudson, 1972; Lin & Hudson, 1976). SEP protons may contain 10% of the total flare energy (Mewaldt et al., 2008). Ion energy in the impulsive phase may compare with electron energy (Ramaty et al. 1995). Ramaty et al Mewaldt et al. 2008

Action at a Distance In resistive MHD models, Ohm’s Law imposes the requirement of local heating. This is not what we observe! Particles can have enormous ranges, approaching the physical scale of the corona. Models this superficial may be forced to resemble the data, but can never self-consistently describe the physical processes involved with any precision. The several strong lines of evidence that particles contain important parts of the flare/CME energy – most of the impulsive-phase energy – means that we cannot ignore their property of “action at a distance”.

Conclusions Highly accelerated non-thermal particles dominate the energetics of all phases of a solar flare. The particles have long stopping ranges, and the energy they transport does not dissipate locally. Flare theories and models need to account for this “action at a distance.”

Extra stuff

Courtesy Jiong Qiu

Sun, 2010